Automatic baby swings powered by electric stepping motors have been in widespread use for many years.
In some prior swings, a desired swing amplitude (angle) can be selected by the user turning a dial mechanism between different predetermined settings to adjust the electric power supplied to the motor. However, it is necessary to compensate for weight differences between different babies or possibly arising from other external variables such as changing wind resistance from the size of a child or prevailing weather conditions which result in unwanted changes in swing amplitude.
In one prior approach taught by U.S. Pat. No. 6,339,304, issued 2002 to Allison et al, the disclosure of which is incorporated herein by reference, compensation is provided by automatically varying the power applied to the motor when the actual swing amplitude deviates from a preselected swing amplitude. However, Allison requires an additional mechanical device comprising a series of light interrupting prongs mounted for movement by the swing between an IRLED and a photodetector and means for counting the number of resulting light interruptions which varies according to the swing amplitude. Such approach may be regarded as relatively cumbersome and possibly not wholly reliable over the swing life, as a result of the requirement to maintain accurate mechanical alignment of the prongs between the LED and the photodetector.